Adding arduino Metro RP2040 SD card example

Adding Arduino SD card example for Metro RP2040

Author: BlitzCityDIY

Adafruit_Metro_RP2040/Arduino/Metro_RP2040_SD_Card_Test/Metro_RP2040_SD_Card_Test.ino

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+// SPDX-FileCopyrightText: 2023 Liz Clark for Adafruit Industries
+//
+// SPDX-License-Identifier: MIT
+/*
+  SD card read/write
+
+  This example shows how to read and write data to and from an SD card file
+  The circuit:
+   SD card attached to SPI bus as follows:
+   ** MISO - pin 20
+   ** MOSI - pin 19
+   ** CS   - pin 23
+   ** SCK  - pin 18
+
+  created   Nov 2010
+  by David A. Mellis
+  modified 9 Apr 2012
+  by Tom Igoe
+
+  This example code is in the public domain.
+
+*/
+
+// SPI0 pins for Metro RP2040
+// Pins connected to onboard SD card slot
+const int _MISO = 20;
+const int _MOSI = 19;
+const int _CS = 23;
+const int _SCK = 18;
+
+#include <SPI.h>
+#include <SD.h>
+
+File myFile;
+
+void setup() {
+  // Open serial communications and wait for port to open:
+  Serial.begin(115200);
+
+  Serial.print("Initializing SD card...");
+
+  // Ensure the SPI pinout the SD card is connected to is configured properly
+  SPI.setRX(_MISO);
+  SPI.setTX(_MOSI);
+  SPI.setSCK(_SCK);
+
+  if (!SD.begin(_CS)) {
+    Serial.println("initialization failed!");
+    return;
+  }
+  Serial.println("initialization done.");
+
+  // open the file. note that only one file can be open at a time,
+  // so you have to close this one before opening another.
+  myFile = SD.open("test.txt", FILE_WRITE);
+
+  // if the file opened okay, write to it:
+  if (myFile) {
+    Serial.print("Writing to test.txt...");
+    myFile.println("hello metro rp2040!");
+    // close the file:
+    myFile.close();
+    Serial.println("done.");
+  } else {
+    // if the file didn't open, print an error:
+    Serial.println("error opening test.txt");
+  }
+
+  // re-open the file for reading:
+  myFile = SD.open("test.txt");
+  if (myFile) {
+    Serial.println("test.txt:");
+
+    // read from the file until there's nothing else in it:
+    while (myFile.available()) {
+      Serial.write(myFile.read());
+    }
+    // close the file:
+    myFile.close();
+  } else {
+    // if the file didn't open, print an error:
+    Serial.println("error opening test.txt");
+  }
+}
+
+void loop() {
+  // nothing happens after setup
+}